Wire antennas may be grouped into two categories: resonant, and non-resonant or terminated. The common half-wave dipole is an example of the resonant antenna while a rhombic antenna is an example of a non-resonant type. In a resonant antenna current flows back and forth, reflecting from each end, while in a non-resonant antenna the current flows once through and is absorbed in a load, usually a resistor equal to the impedance of the antenna viewed as a transmission line. For a given length of wire, resonant antennas are more efficient, but they suffer from narrow bandwidths and broad radiation patterns. Non-resonant antennas function over a very wide range of frequencies, and can be made extremely directive when made long in terms of the wavelengths being radiated.